The EMD engine, manufactured by Electro-Motive Diesel, is a two-stroke diesel engine. It is a medium-speed engine, used in locomotive, marine, and stationary power applications. The engine is made in V-8, V-12, V-16, and V-20 configurations. Most current locomotive production is the V-12 and V-16 version of the engine, whereas many of the marine and stationary engines are V-20 versions.
In addition to being a two-stroke diesel engine, the EMD engine is a uniflow scavenged engine. The engine requires an external air pump to provide enough differential air pressure across the cylinder to allow the engine to be scavenged correctly.
For an EMD engine, two different air pump systems have been used. A “naturally aspirated” engine has a gear-driven roots-type blower. A “turbo-supercharger” engine has a gear-driven turbocharger. The gear-driven turbocharger provides the required air flow at idle and light-to moderate loads. At higher loads, once the exhaust energy is high enough to sustain the turbocharger, an overriding clutch releases and the turbocharger “comes off the gear” maximizing engine efficiency.